Fourier domain optical coherence tomography (OCT), which employs the wavelength swept fiber laser source can be the most suitable OCT system for commercial purposes in biomedical imaging. Standard swept source OCT system generally requires some scanning mechanism for three-dimensional imaging to provide high resolution, high sensitivity, and cost-effective system. However, for some applications, the scanning swept source OCT may not be suitable due to the following issues.
First, imaging speed has a fundamental significance not only because of the high demanding of real-time information, but its relationship to detection sensitivity (e.g. minimum detectable reflectivity). The scanning OCT obtains a three-dimensional image with point to point scanning, and thus provides slower imaging speed than full-field OCT system. In order to increase the imaging speed, a more complicate and expensive high-speed tunable laser can be used. Moreover, as an A-line rate increases, detection bandwidth is generally increased proportionally, and therefore the sensitivity drops. Although increasing the laser source power would, in principle, improve the sensitivity, available laser sources and maximum permissible exposure levels of tissue represent significant practical limitations.
Second, a maximum imaging depth in tissues of all OCT is limited to a few millimeters due to the absorption and scattering of biological tissue. Consequently, a passive probe for endoscopic OCT imaging is highly desired. Currently, most scanning probes in OCT systems can be divided into two categories: I) probes using MEMS (microelectromechanical systems) mirror for front view two-dimensional scans; and II) probes using a rotating mechanism for lateral view two-dimensional scans. Using MEMS mirrors can more suitable for brain imaging where front view is preferred. However, rotating MEMS mirror at a distal end of an OCT probe means that every OCT probe using a MEMS mirror has its own scanning system. When such OCT scanning probes are meant to be disposable, the cost can be too high to justify such disposal and yet there may be no choice but to dispose to prevent cross-contamination of patients. Furthermore, parallel probes using MEMS mirrors can further require sophisticated engineering, which can prevent their use with real-time imaging systems.